OBJECTIVES: The mode of packaging nucleosomes within the eukaryotic nucleus will be investigated using the electron microscope. To preserve the fragile ultrastructure of these higher structures of chromatin, methods involving freeze drying and surface replication will be used. The use of specific antibodies for localizing chromosomal proteins at the ultrastructural level will be explored. A number of methods of overcoming the problem of visualizing the bound antibodies will be used, including decoration with protein A, goat antirabbit IgG, or ferritin-conjugated antibodies, vacuum drying from glycerol, and formation of nucleosome-antibody-nucleosome dimers. The mode of replication of chromatin will be studied using cultured chinese hamster ovary (CHO) cells. Previous work using Tetrahymena indicated that newly synthesized histones were deposited at random on chromatin. This controversial result will be tested in the CHO system.